I think of that 3-4 month period following the births of my three kids as The Twilight Zone (can you hear the music, too?). Everything, for the most part, is a haze, and it’s not because the kids were born 8, 12 and 14 years ago. My brain, at the time, more than likely was having a “hormonal bath.”

For many women, births trigger chemical changes to the brain, in addition to obvious changes to the body. Researchers at The Kinsey Institute at Indiana University Bloomington and their colleagues in the College of Arts and Sciences consider this postpartum period prime for study. It can provide a better understanding of the survival of our species – and the survival of couples’ relationships.

“We’re particularly interested in what accommodations people have to make when they have kids — men and women — and the stresses,” said Julia Heiman, director of The Kinsey Institute. “It’s been studied, but how then do other emotional features, relationship factors and sexuality fit in? These have been neglected even though they’re important to relationships.”

It’s common, for example, for new mothers to be uninterested in sex during the six months following a baby’s birth. Sometimes this is described as a dysfunction. There’s more to it, though, than women being sore and frazzled.

In a Kinsey Institute study that examined this question, some of the postpartum women who looked at arousing sexual images found them anything but arousing. It wasn’t something like, “Well, that looks like fun if I weren’t so tired.” It was more like, “Yuk.”

The “findings emphasize the complexity in the mechanisms underlying fluctuations in women’s reproductive priorities,” Heiman and her collaborators wrote in a journal article published recently in Hormones and Behavior. The lead author is Heather Rupp, research fellow at The Kinsey Institute. “We believe that decreases in sexual desire during the postpartum period may less be considered a dysfunction or problem and more positively as behavioral neuroendocrine change characteristics of the postpartum period warranting further investigation.”

The researchers are particularly interested in how the hormone oxytocin influences mothers’ brains. They have conducted experiments where they take images of the brains of new mothers and nulliparous women — women who have never had children — after having them look at pictures designed to elicit certain kinds of reactions, and after administering oxytocin to some.

Julia Heiman

Oxytocin, which is released in greater amounts during and after childbirth, is known to play a powerful role in a healthy mother’s unique state of mind by providing a calming effect when mothers breastfeed and by heightening interest in baby-related threats.

In their Hormones and Behavior study, the researchers expected to find that postpartum women, when compared to the other women, showed a stronger reaction in their amygdala, the part of the brain that controls emotional response, to images involving babies and a weaker reaction to sexual images. This would fit evolutionary models that anticipate trade-offs and priorities.

In reality, however, the postpartum women showed less reaction to all the images, including those of the babies (generally pleasant images, not threatening) and pictures considered neutral. When the postpartum women were asked to subjectively rate their reaction to the images, the results were as expected, with reports of less reaction to sexual images but stronger reaction to baby images compared to the other women.

“We interpret these data to suggest that decreases in self-reported feelings of sexual desire in postpartum women are related, in part, to a generalized decrease in amygdala responsiveness to arousing stimuli rather than a sex-stimulus specific change in brain function during the postpartum period,” they wrote.

This blog post discusses the team’s findings in another study that looked at how oxytocin might influence how postpartum mothers react to threats both related and unrelated to babies.

The research is expected to provide a better understanding of factors that contribute to postpartum depression, which can be debilitating and even deadly, and to provide insights into adaptations women undergo as they and their partners move on with their lives while building families.

“The amount of adaptation and accommodation and incorporation of complexity and feelings in life has been underappreciated,” Heiman said. “We need to appreciate this period, not just celebrate or criticize.”